Development and course of tuberculin allergy in guinea-pigs vaccinated with various doses of Danish liquid BCG vaccine.

BCG vaccine is commonly assessed for biological activity by its ability to induce tuberculin sensitivity in guinea-pigs. In 1950, the WHO Expert Committee on Biological Standardization advocated using a sensitizing dose of 5 mg of BCG. It is now known, however, that allergy can be produced by much smaller doses. Since the use of such a low dose that an attenuated vaccine would fail to induce allergy might be advantageous for assessing the biological activity, a further investigation of tuberculin allergy in the guinea-pig has recently been undertaken jointly by the BCG Department of the Statens Seruminstitut, Copenhagen, and the former WHO Tuberculosis Research Office, Copenhagen.As a first step in this investigation, the presence and degree of tuberculin allergy were studied in relation to the dose of BCG administered. The results, presented here, showed that in guinea-pigs, unlike in humans, the production of allergy is to a large extent independent of the vaccine dose. On the other hand, the speed of development and the maximum allergy attained are functions of the dose. It is suggested that the speed of allergy development and the median effective dose in guinea-pigs might be used as criteria for assessing the biological activity of new batches of vaccine.